The wire supports to which the invention is directed have been used with good results in the well-known tungsten halogen type of lamp which comprises an elongated tubular envelope having an axially extending filament. These lamps are frequently referred to as quartz iodine lamps and are available in T2, T21/2, T3 and T4 sizes, the numeral indicating the external diameter of the envelope measured in eights of an inch. The lamps are very compact and are made in various wattage ratings up to several thousand watts. Their spectral emission is such that they can be used either as light or heat sources.
The wire support members are anchored to the filament at spaced points and include an outer loop disposed in encircling spaced-apart relationship which engages the envelope wall to maintain the filament on axis. Such supports, and a coiling spindle or mandrel for winding and installing them on the filament are shown in U.S. Pat. No. 3,168,670 to V. C. Levand. Improved more automated apparatus for coiling and installing such wire supports and which is more economical of the quantity of wire used is disclosed in U.S. Pat. No. 3,556,169 to J. B. Yoder.
An ever present problem with the support designs and apparatus available up to now has been springback of the wire upon severing the finished support from the supply or upon release from the forming mandrel or spindle. The wire is resilient and must be so in order to adequately perform its support function. Inevitably this means that the outer turn of the support which is disposed in encircling relationship to the filament unwinds and expands in diameter upon release. By way of typical example, in a spiral-wound wire support such as formed by the Yoder apparatus, the expansion of the outer turn upon release from the forming mandrel may be as much as 30%. The outer turn of the supports must be sized to enter readily into the lamp envelope at assembly and fit snugly without excessive play. Accordingly, a winding mandrel is provided of such diameter that the support is properly sized after release and springback. However, the difficulty arises from the fact that the degree of springback increases with resiliency and is also an inverse function of wire size. In other words, a finer or a stiffer wire has more springback which must be anticipated in the design or in the machine adjustment. Since the wire size may need to be changed and since unavoidable manufacturing tolerances allow some variations in size and resiliency or temper, maintaining the wire supports within the size limits has been a continuing problem.